Attempts to prepare Si.sub.2 N.sub.2 O are known, for example from R. Marchand and J. Lang, C.R. Acad. Sc., Paris, 1967, Vol. 264. Ser. C., p. 969-972. It appears from this article, however, that a complete conversion to Si.sub.2 N.sub.2 O was only achieved after four days at 900.degree. C.; moreover, the starting material was obtained via a complicated and costly method of preparation. In particular, the starting material was prepared from [Si(NH).sub.2 ].sub.nx, which was prepared by the reaction of SiCl.sub.4 with NH.sub.3.
Moreover, from more recent literature for example the Journal of the American Ceramic Society, Vol. 66, No. 11, November 1983, p. 761, it was known on the other hand that a pure silica gel heated to 1090.degree. C. in flowing ammonia produced a final product with a maximum of only 0.5 wt. % nitrogen, while on the other hand the only conclusion that an expert up to now could draw from recent literature, for example Mat. Res. Soc. Symp. Proc., Vol. 73, 1986, Materials Research Society, pp 559, is that there is still clearly no economic and reproducible method for the preparation of Si.sub.2 N.sub.2 O, so that despite the close structural similarity between Si.sub.3 N.sub.4 and Si.sub.2 N.sub.2 O, high-grade materials based on Si.sub.2 N.sub.2 O have not received much attention up to now. It was found from recent experiments, for example, that although the nitriding of a mixture of silica and elementary silicon in a controlled atmosphere containing nitrogen and oxygen with metal oxide as catalyst resulted in the formation in Si.sub.2 N.sub.2 O, a considerable quantity of silicon nitride (.about.15%) was also formed and a quantity of unreacted SiO.sub.2 remained.
It will be appreciated, therefore, that there is still no economic and reproducible method for the preparation of pure Si.sub.2 N.sub.2 O using relatively cheap and plentiful starting materials.
An object of the present invention is therefore to provide such a method of preparation in order to meet a very rapidly growing need for this product for a number of potential high-grade technical applications, such as for high quality ceramic materials and industrial catalysts and/or catalyst carriers.